Distribution of actinomycetes in different soil ecosystems and effect of media composition on extracellular phosphatase activity

Abstract

Actinomycetes are widely distributed in different habitats and involved in important processes. Therefore, evaluation of their distribution is important in understanding their ecological role. Ninety seven samples were taken from different soil ecosystems (forest, pasture, rain-fed and irrigated cultivated land) located in various climatic zones in the province of Golestan, Northeast Iran. The number of actinomycetes as well as pH value, organic carbon (OC) and soil salinity expressed as electrical conductivity (EC) showed significant differences in the soil ecosystems under investigation. The number of actinomycetes decreased from 2.86 * 10 6cfu g-1 in irrigated cultivated land to 7* 105 cfu g-1 in pasture (p<0.01). In pastures, the number of actinomycetes was negatively correlated with EC (r=-0.60, n=15, p<0.001) and pH (r=-0.59, n=15, p<0.001). In other soil ecosystems under investigation no significant correlations between soil pH, OC and EC and the number of actinomycetes could be found. In forest soils, the number of actinomycetes was significantly dependent (p<0.05) on climate. A significantly higher population was observed under semi-arid conditions compared to all other climatic zones (humid, sub-humid, Mediterranean). Because many soil microorganisms are able to transform different forms of insoluble organic and inorganic phosphorus into a soluble form suitable for plant uptake, the capacity of the isolated actinomycetes to secrete phosphatase activity was determined under laboratory conditions. A huge variation in the capacities to produce acid and alkaline phosphatases among the different isolates was observed. These enzyme activities and the capacities to hydrolyze phytate in the fermentation broth were significantly dependent on medium composition. In general, substitution of arginine and glycerol in the modified glycerol arginine medium (MGA) with other nitrogen and carbon sources resulted in a significant reduction of phytate dephosphorylation.